Human factors design in telephony
Citation for published version (APA):Leopold, F. F. (1970). Human factors design in telephony. Kansas State University.
Document status and date: Published: 01/01/1970
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'
•
HU
FACTORS DESIG
•
F.
LEOPOLD
lnstitute for P reeption Research Eindhoven, t e Netherlands
lAL REPORT NUMBER
89
KANSAS ENGINEE ING EXPERIMENT STATION
KANSAS
STATE UNIVHSITY
MANHAnAtt KANSAS 66502
TELEPHONY
F,F. Leopold
Institute for Perception Research Insulindelaan 2
Eindhoven 4501, the Netherlands
Visiting Professor 1970 Kansas State University
Department of Industria1 Engineering
Author's Note
This artiele is derived frorn sorne lectures given during the author's stay as visiting professor in the Department of Industrial Engineering at Kansas State University, Manhattan, Kansas, during the spring sernester of 1970. He is grateful for the stirnulating interest frorn both faculty and students in the field of hurnan factors in telecornrnunication and this artiele should be an irnpetus to students for further experirnents during their courses.
It is generally accepted that information transmission systems should
be optimized with respect to man. However, we abserve on one hand an increasing
number of new systems being made available to a growing number of users who are unfamiliar with such systems; while on the other hand, the increased cast of central equipment makes it imperative that such systems be handled only by
highly trained operators. Even though man is willing and prepared to learn
and adapt, his limited ability to store information and to operate rapidly
make him the weakest link in any communications system. This problem faces
bath the development engineer and the human factors researcher - bath aim at an optimal man-system relationship.
However, the de fini tion of "optimal" in this respect is of ten blurred
as are the means by which such an optimal interaction can be achieved. Teehuical
development aften runs ahead, the goal being to make systems faster, more
reliable and less expensive. This scarcely leaves the human engineer time
to strew a human factor flavor over the boundary line between operator and
machine. In turn, the human engineer, due partly to a lack of technological
knowledge, might fail to anticipate the development of a new system. Moreover,
engineers aften underestimate people's ability to improve, or to make use of possibilities beyond the well known concepts of human mobility and perception.
This paper is a summary and a plea.
It is a summary of work done by numerous psychologists and engineers all over the world in an attempt to imprave the relation between a man and a system. Impravement can be made for the benefit of operators and customers, as well for the efficiency of system and equipment.
It is a plea for an everlasting alertness. Man does change and rnan's
that human factors in telecommunication were studied. Existing systems can
be changed. In that respect we should develop a critica! or even aggressive
attitude. "The Challenge of the Seventies" has perhaps become a platitude
but a decent existence of man in a future society will depend more and more on telecommunication--not only between man and man but also between man and system.
The Past
The telephone, even in its simplest form, was the first complex tool
in the home. Early designers were not concerned with ease of eperation of
the crank or earphone and major attention was given to abundant ornaments,
made possible by new technologies. The switching engineer was more anxious
that the equipment worked rather than whether it worked efficiently. The transmission expert was happy that oral sounds could be transformed into electrical pulses and that transmission performance was sufficient to allow a normal conversation.
The introduetion of automatic exchanges, enabling the customer to dial
the desired party himself, had two important consequences. First, the waiting
time was, with respect to the exchange, determined by the capability of the central equipment and, second, the efficiency of the central equipment was
completely dependent upon the subscriber's performance during dialling. Field
observations in exchanges were used to measure the subscriber's performance but much of the user's behavier was beyoud the cbserver's field of vision. New transmission techniques (e.g. bandwidth restriction) were adopted but again, only incidentally were customer's reactions to such features collected
by questionnaires or interviews. It is only in recent years that, through
fundamental and applied research, we have tried to analyze all humanly
companies or equipment manufacturers employ specialized human factor groups.
In telephony, as in computers, we find hardware and software. The telephone
set is the hardware. The software includes eperating instructions, directories,
time signals, etc. For an onderstanding of research being done and questions
still to be answered, the actions of a person making a call will be followed, step by step.
The Present
Information. Although a telephone set is easy to operate, it is clear that
the user's performance during dialling determines the efficiency of the
exchange(!). Therefore, clear and unambigious directions should bedelivered
with the telephone set and similar instructions should be printed in the
directory, possibly in several languages. Although insome countries
telephone instructions are incorporated in public schools programs, this
idea should be accepted in more countries(2). Such instruction should discuss
the handling of a telephone, pronunciation, planning of the conversation, as wellas some technica! information on how the equipment works.
The subscriber, wishing to make a call, will usually take a directory
to locate the party's name and number. A number of diverse human factors
come into play: ,.,rhat type face and size of type should be used for a wide
variety of user,: ,; g a wi.de variety of visual acuity, should the number
be printed before or ufter the party's name, and how should a number be grouped
to facilitate the memorization. Obviously, the more entries per page, the
lower the cost to pro .. J~e he directory. The cost of the directory must be
balanced by the cos': of ncreased inconvenience and errors by the cus tomer. In some countries mud: attenLion is paid to an optimal instruction and infomation presentat" on ot a directory.
Very often, however, a letterhead is the souree of the number to he called. The CCITT will establish recommendations as to how a telephone number
should he printed, especially for mail going abroad. Special multilingual
instructions in directories and telephone booths should enable the foreigner
to place calls himself. The fact that there are basic differences between
systems in various countries is a handicap and makes unambiguous instructions
imperative. Experiments in different countries will probably lead to an
*
international standard (3) •
Making the Call. The next step in making a telephone conneetion using a
standard phone set is picking up the receiver. The receiver's dimensions
should fit a wide variety of people, each having his own anthropometric properties. Measurements have been made of different populations: width
of handpalms (handpart of receiver), diameter of fingers (holes in the dial,
dimensions and center to center distance of keys), eye levels (mounting
height of telephones in booths), etc.
The moment a receiver is lifted, the peripheral telephone is connected
to the central processing equipment in the exchange. This is indicated to
**
the subscriber by a tone signal, the first dialling tone Since the subscriber
usually is not charged for this conneetion (nor for the total dialling procedure) administrations try to put an upper limit on the time lapse between lifting
the receiver and the first digit dialled and the time lapse between dialling successive digits. This limit prevents misuse of the telephone (receiver lifted and laid down next to the set, receiver improperly positioned * The C.C.I.T.T. (International Consultative Committee for Telephony and
Telegraphy) in Geneva sets standards for equipment and transmission. Working party II/5 is involved in recommendations for all human aspects. **"First" dialling tone because in some countries e.g. in Sweden and the
Netherlands a second dialling tone is used between the exchange number and the subscriber number.
after use, cleaning, long hesitations during dialling and incomplete
dialling). Field studies showed that under normal conditions the time
of the first dialling tone has a positively skewed distribution. Most
countries have arbitrarily set an upper limit on the time allowed for the subscriber to start building his conneetion and on the time lapse between
the digits called. If this time is exceeded, the subscriber is disconnected
from the exchange equipment and a busy signal or verbal announcement is given.
The most crucial step making a call is the dialling. The two main parameters
the telephone administration is concerned with are the dialling speed and the errors made by the user during dialling. The errors result either in a wrong conneetion or in an incomplete number (if the user is aware of
having made an error, stops dialling and replaces the receiver). Errors
can have different origins: the number may he remembered incorrectly, or
may he misread in the directory, or may result from false manipulation of the dial (the finger is placed in the wrong hole or slips out of the hole when rotating the dial).
In the United Kingdom and the United States, studies have been performed
camparing different alternatives in indicating the 10 holes in the dial (4).
An unambiguous conclusion cannot he drawn because, depending on the criterion
(speed, errors), different solutions seem to he optimal.
The introduetion of push-button dialling changed the telephones' appearance
completely. The first experimental key set telephones used a circular
arrangement of keys in the same way and sequence as the holes in a dial were
arranged. It was questionable, however, whether that layout was optimal
for speed of keying, error percentage, and for the electrical structure of
the phone. After a careful comparison of different layouts during experiments
Company adopted the 1 2
4 5
7 8
0
3 arrangement for its touch-tone system.
6
9
Other important factors are the center to center distance of the push
buttons, their dimensions and the force-displacement curve. Most
recom-mendations are a campromise between human and electrical engineering con-siderations.
In the Netherlands, where the first public push-button exchange soon will be put into use, the question arose how fast a subscriber would key
a number of the typical Netherlands composition. In the Bell studies, a
7-digit subscriber numbering system was used. In the Netherlands, however,
long distance telephone numbers show 8 to 10 figures. In two studies
the user performance was measured both with a rotary dial telephone and a
key-set telephone. In the first study, the subjeet's task was to find a
telephone number of a particular person in a part of a directory page (Fig. 1), to remember both subscriber number and area code, and finally
to dial or key the number in question. The results showed that performance
on the push button set was twice as fast as on the dial telephone and that the error percentage (numbers showing at least one error) was not significantly
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HOUTH NV v/h J T MEINESZ Vert P Streatsma A d Hoven 111 bov . , . 0 •
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HUISHOUDELIJKE VOORL ten PLATTE-LANDE Mei T J Bergs ma Händelstr 14. HUISHOUDSCH KATH GrKerkstr89. o o
HUISHOUDSCH LEEUW IND en
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Fig. 1 Part of a page from the directory. The subscriber to be called
~-,'as Houttuin, J. His number was 0165 7-29438. Note the different
format from American directories.
Set
Taûle 1.
Average presentation
time in
Responses to dialling and keying imputs
I
. Average Percentage Percentage
Average Percentage
! time 1st wrong wrong
dialling tone exchange subscriber
I
selection time wrong
in seconds numbers
--·--· __ ..
--~_l
____
s_e_c_o_n_d_s_· --c-' __~_·n_se_c_o_n_d_s·---+---:---:---n_u_m_b_e_rs
_ _ _, ___n_u~._b_e_r_s
_ _ Di al Key 37.9 38.8 1.8 1.7 20.4 11.3 4405% 43o6% 21.4% 2000% 3306% 3401%dialling and keying while the numbers remained visible. Moreover, this study was clone on six successive days to see how performance improved with
training. Again keying was twice as fast as dialling and again error
per-centages were notdifferent (See Fig. 2). A striking observation was made
during the sixth day when actuation times (the time that a particular key is
SEC 16 15 14 13 12 11 UJ 10 ~ 1- 9 z B 0 1-u 7 w -' w 6 V) 5 4 3 2 0 ~ ~ ~
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4 5 6DAYS TIMEFig. 2. Mean dialling times (seconds) for six subjects on six successive
generating the information to the exchange) were measured. It seems that even comparatively untrained users are able to perfarm times as short as
30-40 msec. (Fig. 3). If future exchanges are not able to process such short
duration information, we may anticipate a considerable number of incomplete
0/o 4 0 . - - . - - - . - - - , - - - , - - - , - - - , - - - . - - - , - - - , - - , ----r----+---+---+--.~--~--~~--~--~ f---t----+--t---t---,
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0 __. 0 10 20 30 40 50 60 70 80 90 100MS PULSTIMEFig. 3. Frequency distribution of actuation times (milliseconds). The
means are for six subjects on the sixth day of the secend study.
keying actions. Because it is not advisable to draw-decisive conclusions
from experiments in laboratory conditions, a number of observations were
made in a PBX exchange. In general they confirm the experimental values.
Feedback during connecting. Once the dialling is completed, the user expects
*
to hear a tone signal, either the ringing done or the busy signal. If such
signal is presented only after a delay, telephone administrations should indicate this in the directories so that foreigners, not familiar with such
systems, don't become confused and replace the receiver. In international
dialling (and this will soon be common place)(6), tone signals used in ether
*
Insome countries (France, England, Netherlands, etc.) additional signalsare used, e.g. for a faulty line or when a subscriber's conneetion has been disconnected.
countries can differ considerably from those used in the originating country. At present there is some evidence that a number of international calls are not completed by the customer himself because he is confused by strange
sounding tones, making him unsure so that he hangs up and consults an operator. This problem has been recognized by the CCITT and an attempt was made to
set standards for tone signals to minimize the future customer's confusions and errors.
To obtain more data on the human factors requirements to such standardized tones, the Bell Telephone Laboratories designed an experiment during which a great number of commonly used and unfamiliar telephone signals were presented. Parameters were modulation, frequency, repetition period and the ratio of "signal on" period to repetition period. Subjects had to state whether the signal presented sounded like "busy", "ringing" or "neither busy nor ringing". After being performed with American listeners this experiment was replicated in 8 other countries, a unique international collaboration in the human factors field of research.
The general conclusion seems to be that repetition period mainly determines whether a tone sounds like "ringing" or "busy"; frequency and ratio tend to be
relatively ineffective as cues for "ringing".
An additional experiment was performed in the Netherlands and the United Kingdom, the aim being to find an optimal instruction methad to make sub-scribers familiar with tone signals in countries they want to dial to. Such instruction can either be given in printed form, in which the signals are described in subjective terms (e.g. as a special note in the directory)
ar in a recorded form in which case the subscriber can dial a special
number after which a recorded voice will explain how to dial, with additional specimens of foreign tone signals. The results demonstrated that both
printed and recorded information helped to reduce the confusion caused by such signals. For financial considerations a printed instruction is preferred and recorded instructions should only be given for those countries in which the signals differ considerably from the signals with which the subscriber is familiar. It should also be pointed out that in some countries (as in the United States) i t may take several seconds after having finished dialling befare a tone signal is heard(?). Other investigations considered the
tolerable levels of tone signals, heard under different conditions of
. 1 . (8)
env1ronmenta no1se.
Once the conneetion with the required party has been established, that party will be signaled by a bell coming from the telephone set (or by
additional signals depending on the situation). The bell, having a wide frequency spectrum, is generally accepted for this purpose. Experiments in field
conditions showed that a bell is effective against a wide variety of background noises. When questioned, however, a majority of the subscribers tend to
prefera tone signalover the conventional bell(g). More experiments should determine what tone spectrum has an optimal acceptability, how aften subscribers use a volume adjustment and what the effect would be of tone signals which
become lauder with each successive ring. For future telephone circuits,
tones have electronic advantages over the bell, now in general use. An inherent problem is the time needed by the called party to hear the signal and to
reach the telephone set. This time is also affected by the number of extension telephones in a home or by the existence of extension ringers. The distribution of ring tone times has been determined from observations in exchanges. It
depends on the administration's policy whether, after a certain waiting time, the subscriber is disconnected automatically from the not answering party.
Another feature having many teehuical and human factors implications that is being considered by some administrations is a signal given to a subscriber using a line indicating that another party wants to be connected.
Conversation: Once the conversation is made possible, the telephone
administration has little influence with respect to the efficiency of that
conversation. (10) Their recommendations advise the subscriber to prepare
his talk carefully, to report himself not merely by saying '~ello'' but rather
by giving name or telephone number, etc., etc. As much boils down to habit,
school training might have a favorable influence.
The quality of transmission is determined primarily by the technical
features an administration is prepared to make available. Loudness at the
receiving end is an important criterion but the loudness level is likely to
vary considerably. Not only can the speech level at the transmitter side
differ but the number of links between the transmitter and receiver can cause
a decrease in volume level to below the audible range. (11) Other factors
influencing the audibility and intelligibility at the receiving end are
signal-to-noise ratio, bandwidth restriction, and distortion. Experiments
have been performed for many years in which transmission engineers and psychologists compared different alternatives.
Finally, echo and propagation times (especially in intercontinental connections via communication satellites) can have a unfavorable effect on
the acceptability of speech communication. Because monitoring of such
conversations is illegal, the subscriber is interviewed afterwards to
obtain his impressions of the comparative ease of communication using radio
links versus cable connections. However, the effect of propagation times
on transmissions performance can be measured and evaluated in simulated
. (12)
Much information about difficulties encountered by foreigners when placing telephone calls in another country will be derived from
question-naires.(l)) These questionnaires will be standardized internationally so
that data from different countries can be compared.
Future Developments
A number of new features having human factors implications have
recently been introduced in some countries and more are coming. It is here
that a plea should be made to both telephone companies and manufacturers for a careful consideration of all human factors involved in new services. Development of new gadgets is no problem in this age of refined technology but aften too little attention has been paid to human implications and too
little thought given to methods of introducing new gadgets. A simple example
may illustrate this. In key set telephony there is essentially no limitation
as to the number of keys. It seems logical to use telephones for purposes
other than for spoken communication and, as a result, some telephone companies
have introduced sets having 2 additional keys, (l4) and have plans to add
another four keys to make a total of 16. There is a problem as to labelling
the additional keys. A survey showed that a wide variety of symbols is in
use in different countries and there is an urgent need for standardization. There are many requirements for such standarized indications. They should not be confused with digits or letters either in form or pronunciation; they should be printable, if possible with a typewriter; in international traffic, labels should not raise confusion in different languages, etc, etc.
In some countries this problem was recognized too late. International
Although not cornmonly in use at this moment, some countries offer access to special facilities such as abbreviated dialling. By operating an additional key, the telephone set is connected to a memory in which up
to ten frequently called numbers are stored. Each one of the normal
numbered keys corresponds with one of the numbers in the memory so that
b y s1mp y touc 1ng one . 1 h" k ey a connect1on can e o ta1ne . . b b . d (lS) A refinement
of this system is a device that, in case the other party is busy, repeats
calling the required number until a conneetion can he completed. But even
more possibilities are disclosed by extending the 10 digit keyboard. The
telephone, except for its key arrangement, is similar to the desk calculator and can easily he used as an input unit for all types of data processing
systems. Such links, feasible at this moment, should he tested very carefully
in simulated situations. Much depends on whether the operating party is
a specially trained or is an average subscriber, making use of the facility only
incidentally. All conventional computer input systems have a direct or short
term delayed feedback (cathode ray tubes, indicator tubes, printers) so that the operator can check for himself what data he has submitted to the system. Using the telephone, however, such visual feedback indication would he
missing. Although special tone signals could he made available for all
steps in transmitting a message, too wide a variety of signals can increase confusion so this seems not advisable.
In experiments using a normal telephone to remit money from one account
number to another account number, two procedures were compared. The most
elaborate procedure used a verbal (computer activated) verification, irnmediately after a certain number or amount was keyed, enabling the subscriber to check
provided only a "proceed-to-send" information. The results indicated that it is possible to use a key set telephone as a low speed data transmitter; however, it was observed that the spoken (and time consuming) repetition
of groups of digits by the computer for the purpose of verification contributed little in the detection of certain errors made by the subscriber* Also, from other experiments in this field, it is obvious that data entry with push
button telephones opens a wide field of applications. Much depends, however,
. (16)
on the oparator's tralning.
The way in which a computer should give verification or response to the problems presented depends mainly on the extensiveness of the vocabulary. Fora limited number of words (e.g. the ten digits), voice recording can be
used. For a more elaborate stock, computer synthesized words are applicable.
Phonetics research can provide the essential parameters necessary to make these artificial speech-sounds perceptually acceptable.
The conventional systems input is manipulation on a keyboard. One
wonders how far the human voice, via a speech recognition device, could be used as an input facility for those who are not trained to operate
keyboards. A few experimental voice eneaders seem to give promising results,
(17)
but application on a larger scale is doubtful as yet. Such an encoder
would need to "understand" different dialects or even languages, and this
is a difficult technical problem. From a human factors viewpoint it is
questionable whether an operator is able to pronounee long rows of digits during a prolonged time span.
A new step in human communication is the videophone, transmitting
speech and pictures. Most operating installations so far serve for
experi-*
Some essential numbers, e.g. bank account numbers, can be secured againsterrors by check digits, enabling the computer to check itself whether the
number is existing or not. A subscriber verification of such numbers is
mental, demonstration ar exhibition purposes. It is difficult to anticipate the effect of additional visual information, compared to speech communication only, on the efficiency with which messages are exchanged, but it has been
shown that videophone links are occasionally useful. Special studios will
enable the business community to confer over long distance. Such studios
will have additional facilities such as fascimile transmitters and receivers
. (18)
and spec1al blackboards.
As was discussed before, communication with systems by using a normal
telephone implies an "audio" systems output. A more refined output
pos-sibility is a T.V. monitor on which characters are displayed electronically. Because it is advantageous to use conventional monitors, such characters will be composed of lines and line segments thus giving a character a more
or less stylized farm. Here human factors considerations with respect to
subjective acceptability and objective readability should be evaluated and compared to the teehuical possibilities and the cast of circuitry.
SUMMARY
Although this paper cannot give a complete summatien of all human factors research in the field of telecommunication, it has attempted to indicate a few items.
- The manufacturers of telecommunication systems cannot afford to neglect
the consumer. Although most telecommunication networks in the world are
under supervision of the governments, eliminating competition, it is apparent that customer behaviour, to a large extent, determines the
efficiency of these systems. Both manufacturer and consumer therefore
should cooperate by setting up human factors departments whose main tasks should be studying man in his communication environment and escorting
(19)
development of new systems.
It is often said that telecommunication brings peoples closer. This is
only true if by standardization and international agreement tele-communication systems are compatible not only technically but from a
human standpoint as well. Human factor studies in telecommunication
should be designed and performed on an international basis.
- Border lines between telecommunication and computer systems seem to fade
away. Therefore, human factors experts from both fields of interest should
exchange views and cooperate in the design of new developments. The development engineer must recognize that the final aim of his creations
is the improverneut of rnan's communication. He should therefore accept
the cooperation of the human factors engineer at an early stage and place his technica! knowledge at his disposal during the preparation of human factor's experiments.
1. H. Sylvan A. Gustavii 2. C.J. Wendt 3. E.T. Klemmer R. Conrad 4. F.E. Williams 5. R. Conrad R.L. Deiniger G. Rothert F. Pfleiderer C. Jacobaeus
Gustomer's aspects on modern telephone sets Het P.T.T. Bedrijf
Telephone instruction at Danish schools Het P.T.T. Bedrijf
Grouping of printed digits for telephone entry V. D. E . Verlag
The page format of telephone directories V.D. E. Verlag
Factors in telephone dial design affecting subscribers' dialling errors
Het. P.T.T. Bedrijf
Accuracy of reeall using keyset and telephone dial, and the effect of a prefix digit
Joumal of Applied Psychology, 1958, ~. 285-288
Human factor engineering studies of the design and use of pushbutton telephone sets
Bell System Technical Journal 1960, ~. 995-1012
Influence of dials and pushbutton sets on errors, including the time required for the transmission of numbers
The 2nd Int. Symp. on Human Factors in Telephony, Kopenhagen. 1964
How do subscribers operate dials with different running-down times as compared with pushbutton keyboard
The lst Int. Symp. on Human Factors in Telephony, Cambridge 1962.
Push button dialling
The lst Int. Symposion Human Factors in Telephony, Cambridge 1962.
*"Het P. T.T. Bedrijf" refers to the proceedings of the Third International Synposium on Human Factors in Telephony held in the Hague (the Netherlands)
1966 and published in "Het P.T.T. Bedrijf" Vol. XV. 1/2 Mai 1967. "Het PTT
Bedrijf" is edited by the Netherlands Postal and Telecommunication Services, 12 Kortenaerkade, The Hague, the Netherlands.
"V.D.E. Verlag" refers to the proceedings of the Fourth International Symposium On Human Factors in Telephony held in Bad Wiessee (Germany) 1968 and published by VDE-Verlag GmbH, Bismarkstrasse 33, 1 Berlin 12, Germany.
6. L. Hakansson G. Rothert R. Evers K. Fischer F.F. Leopold H. Stremmelaar R. Conrad C.J. Wendt M. Suzuki A. Armbruster J. Fr~drich K. Fisher H. Leigh
s.
Reinholdsson I. Tange G. Wikell M. S. S choef flerSubscribers' reactions in a Swedish push-button field trial.
Het P.T.T. Bedrijf
Further investigations on the influence of push-button sets on errors and dialling time
Het P.T.T. Bedrijf
Allalysis of laboratory and field tests of dialling habits, particularly with respect to push-button diaHing
Het P.T.T. Bedrijf
A comparative study of human performance with dial and keyset telephones
Het P.T.T. Bedrijf
Performance with different push-button arrangements Het P.T.T. Bedrijf
Same results from a field test on push-button dialling in Gapenhagen
Het. P.T.T. Bedrijf
Customer dialling behaviour during push-button dialling field trial test in NTT
V.D.E. Verlag
Examinatien of the influence of the
force-distance characte~istic and the keyboard slope on
the keying error frequency V.D.E. Verlag
The influence of the strength of the spring on the actuation times of a push-button set equipped with reed cantacts
V.D.E. Verlag
Subscriber reaction to international dialling Het P.T.T. Bedrijf
Studies on subscriber's dialling in international automatic traffic Het P.T.T. Bedrijf
Labaratory studies related to subscriber international dialling. I. Dialling of long digit sequences
8. 9. 10. 11. 12. F.T. Leopold H.M. Mevissen H.W. Ouweleen H. Stremmelaat P.B. Cohen M.S. Schoeffler G.P. Kidd R. Martin H.J. Mevissen H. Stremroelaar H. Sylvan S. Pettersson D.L. Richards J. Hutter E.A. Ericsson P.T. Brady D.L. Richards J .E. Karlin HET. P.T.T. Bedrijf
A study on the influence of listening to recorded examples of tone signals or written descriptions of tone signals on the confusability V.D.E. Verlag
The effect of minimal verbal instructions on the interpretation of audible tones
V.D.E. Verlag
The determination of tolerable levels of exchange service tones
V.D.E. Verlag
Customer reactions to tone callers Het P.T.T. Bedrijf
A study of subscriber appreciation of the call signal in a fully electronic telephone exchange network
V.D.E. Verlag
Differences in speech times in different
parts of Sweden and for various types of telephone calls Het P.T.T. Bedrijf
Communication efficiencies of speech links: Possibilities of automatic measurement V.D.E. Verlag
Automatic monitoring of subscriber conversations V.D.E. Verlag
Objective measurement of telephone speech levels and on-off patterns
V.D.E. Verlag
Transmission performance of telephone connections having long propagation times
Het P.T.T. Bedrijf
Measuring the acceptability of long delay transmission circuits used during the "Early Bird" transatlantic tests in 1965
13. 14. 15. 16. 17. 18. 19. 11 H.D. Hohne J.P. Ducanson J.J. Kramer H. Mantel H. Wozny G. Zeidler K. Fischer J.J. Kramer W. Bezdel R.E. Hawken J.W. Allnatt K. Fischer H. Ebel D. Pearman H.A. Iddles H. Ebel A.W. Ayers
Influence of long transmission delays and reverberation on the telephone conversations of testpersons
V.D.E. Verlag
Measurement of user apinion of telephone transmission quality
V.D.E. Verlag
Selection of symbols for the llth and 12th buttons of the push-button telephone
Het P.T.T. Bedrijf
Abbriviated dialling and its probable
efficacy, derived from records of telephone users V.D.E. Verlag
Optimization of operational steps and instructions for navel telephone facilities demonstrated at the abbreviated dialling feature
V.D.E. Verlag
A laboratory experiment on the application of a twelve push-button telephone set of digital data transmission V.D.E. Verlag
Human factors problems in the use of push button telephones for data entry
V.D.E. Verlag
Human factors in the transmission of data
by speech using automati~speech recognition
Het P.T.T. Bedrijf
Subjective studies concerning the viewphone project V.D.E. Verlag
Problems of how to position in front of the videophone
V.D.E. Verlag
Factors affecting satisfactory sound -with-vision conference facilities V.D. E. Verlag
Subjective assessment of picture interference in the videophone V.D.E. Verlag
A survey of human factors research in the British Post Office
